The invention relates to a method and a transmitter for transmitting a message by radio from a transmitter to a receiver, the transmitter transmitting the message to a radio station for message forwarding.
In radio communication systems, messages, for example comprising voice information, image information, video information, SMS (Short Message Service), MMS (Multimedia Messaging Service) or other data, are transmitted with the aid of electromagnetic waves via a radio interface between transmitting and receiving radio station. Depending on the specific embodiment of the radio communication system, the radio stations here can be various types of subscriber-side radio stations or network-side radio devices such as repeaters or radio access points such as base stations. In a mobile radio communication system, at least some of the subscriber-side radio stations are mobile radio stations. The electromagnetic waves are emitted using carrier frequencies which lie in the frequency band provided for the respective system.
Mobile radio communication systems are often configured as cellular systems e.g. in conformance with the GSM (Global System for Mobile Communication) or UMTS (Universal Mobile Telecommunications System) standard, with a network infrastructure including e.g. of base stations, devices for monitoring and controlling the base stations and further network-side devices. Apart from these cellular, hierarchical radio networks organized on a wide-area (supralocal) basis, standards for WLANs are HiperLAN, DECT, IEEE 802.11, Bluetooth and WATM.
Radio stations can communicate directly with one another only if they are both located in the radio coverage range of the other radio station respectively. If direct communication is not possible or, on account of the distance between the radio stations, is possible only with poor quality, then messages between these radio stations can be transmitted via other radio stations which—by forwarding the messages—function as relay radio stations or repeaters. This type of message forwarding can, depending on the specific embodiment of the radio communication system, be carried out both by subscriber radio stations and by network-side radio stations. Messages can be forwarded, for example, in a WLAN between a radio access point and subscriber radio stations located far from the radio access point. Also, in an adhoc mode of a radio communication system, subscriber radio stations can communicate with one another via one or more hops (hop or multihop) without intermediary devices such as e.g. base stations or radio access points being connected between them.
Document WO 2004/107693 A1 describes a communication between a base station and a mobile station via two individual connections: a first connection between the base station and a relay, and a second connection between the relay and the mobile station. A channel estimation is carried out for both individual connections. The forwarding of messages to the mobile station by the relay is subsequently adapted to the channel estimation of the first connection and preferably also to that of the second connection.
The document                B. Rankow, A Wittneben: “On the capacity of relay-assisted wireless MIMO channels”, July 2004 IEEE 5th Workshop on signal processing advances in wireless communications, XP10806099describes a method for radio communication using relays. Here, the source transmits in the first time slot a first signal to the destination and to the relay. In the second time slot, the relay forwards the first signal to the destination and the source simultaneously transmits a second signal to the destination.        